Battery tester and method of testing



Dee. 30, 1941; B, F; w, HEYER 267,826

BATTERY TE STER AND METHOD OF TESTING 2 Sheets-Sheet l Filed Feb. 6,1941 10.5w: um

K INVENTOR. Benjamin 7714 He er 22.59.00 jun Dec. 30, 1941. B. F. w.HEYER 2,257,826

BATTERY TESTER AND METHOD OF TESTING Filed Feb. 6, 1941 2 Sheets-Sheet 2Patented Dec. 30, 1941 uNi'rao; I STATE BATTERY TESTER TESTING ANDMETHOD OF Benjamin F. W. Heyer, 'I'enafly, N. J. Application February 6,1941, Serial No. 377,635

10 Claims.

All automobiles are ncw provided, as regular equipment, with a starter,headlights, tail lights,

stop lights and instrmnent panel lights, and

many with such additional accessories as a radio, cigar lighter,electric fan defroster, fog lights and other convenient gadgets. All ofthese things are operated electrically and entail a heavy drain upon thestorage battery. This is particularly true of the starter which requiresthe sudden delivery of current from the battery of the value of, say,180 amperes or more, and;

sometimes for a considerable period if the motor does not start easily.a

In consequence, sudden battery failure has become a common occurrence,and every motorist is acutely aware that he may not realize that hisstarter is not functioning with its usual energy before it,refuses tofunction at all as the result of battery failure. ing of suchstoragebatteries has become almost a routine matter, and all garages, servicestations and filling stations should be equipped to conduct such tests.

Since tins type of apparatus must be frequently used by men of littleeducation or mechanical skill, it is essential that it be made extremelysimple and positive in operation and indicate correctly the condition ofeach cell in a manner instantly and clearly understandable not only tothe operator, but to the battery owner as well, since such owners arebecoming increasingly reluctant to take the word of the operator that anexpensive replacement is necessary or advisable. Most of the. availabletesting equipmentis based upon the general principle that the internalcondition of a battery is reflected by the internal resistance of eachcell as indicated by the voltage drop across such cell when under load.

The present invention mates to battery testing equipment and methods ofthis same general type, but which is so easy to use that almost anyonecan make an accurate test. The condition of thebattery is indicated bythe position of the pointer of a single meter in a way that will beinstantly and clearly evident and understand- Therefore, the frequenttest-- rated by 20% as compared with its condition when new and fullycharged.

A further advantage of great practical importanceis that the tester canbe produced at such low cost that it can be made available to fillingstations as well as to larger garages and service stations, or the like.

able, not only to the person making the test, but

. also to the battery owner.

The use of a percentage method incomparing one thing with another issimple, clear and graphic to everyone. This invention provides a batterytester which indicates the condition of a battery in percentage with aperfect fullycharged battery. Thus, when the test is made and the meterindicates 80%, the owner is made immediately aware that his battery hasdeterio- As is well known most automobile storage batteries are composedof three cells in series having a normal open circuit voltage ofsomething over six volts or approximately two volts per cell. Also,theyare so designed that when fully charged and under the maximumload forwhich they are rated, the voltage will not drop below 1.8 volts per cellor 5.4 voltsfor the entire battery. A greater voltage drop in anyonecell, beyond a certain point, as compared with any other cellindicates that that cell is defective and,in general, the seriousness ofthe defect is proportional to the magnitude of the voltage drop ascompared withany other cell. Forlthis reason, the condition of' eachcell can be'learned comparatively from the voltage drop when thebatteryis under proper load. I

However, the testis complicated by the fact that the internal resistanceof batteries varies with the number of plates in each' cell, or with thearea of the plates. Thus, a large battery, for example, can deliver agiven current with less voltage drop than a smaller one or a greatercurrent can be delivered with the same voltage drop. Consequently, inthe past when testing a battery, it has been considered necessary toplace the battery under a certain rated operating load beforedetermining the voltage drop across its individual cells. This hasrequired an adjustable resistance in the load circuit capable ofcarrying a.

large current. l

An adjustable carbon pile has been commonly employed for this purpose,as shown, ior example, in my Letters Patent Nos. 1,520,865 and No.2,084,086. Theoretically, the value of the. current flowing in by such acarbon pile to the desired value as indicated by an ammeter. However, asa practical matter, such adjustment cause of the tendency of the pointerof the meter to over-swing. Also, the load circuit is somewhat unstablebecause as the temperature of the carbon pile rises, its resistancechangesso-that the operator must constantly. watch the ammeter andreadjust the carbon pile. Since the battery is under heavy load,-thisadjusting and readjusting may well take long enough to materiallydischarge the battery, so-that the subsethe load circuit can be adjustedis difllcult to make beclearly as by the operator.

' matter, unnecessary. It

'load must be consulted. This is another fertile source of error,particularly in the hands of unskilled operators.

By the present invention the adjustable carbon with a pair-of contactarms I2 and I3, so arpile resistance and ammeter have been supplanted bya resistance of fixed value which may be made of nichrome or other metalhaving a negligible temperature coeiiicient with respect to changes inresistance so that any battery which is connected to this tester willautomatically be placed under a definite and constant load. In addition,an entirely separate voltmeter circuit is provided capable of indicatingdirectly the percentage of difference in condition of each cell of thebattery under test as compared to a perfect battery of correspondingsize. This is done by means of a suitable voltmeter and in a mannerwhich can be understood by the battery owner as easily and Allpreliminary adjustments are made before the battery is put ofpotentiometer I4,

under load. Thus, the actual test can be performed quickly andaccurately without reference to any tables or charts and there is nodanger of discharging the battery to such a degree that the indicatedresults are unreliable.

A form of the invention selected for description herein isshown in theaccompanying drawings, of which:

Figure 1 is a front elevation of the tester;

Figure 2 is a diagram for explanatory purposes showing'an arrangement ofelectrical circuits-- which include a part'of the invention;

Figure 3 is a complete diagram of circuits in which the invention isembodied; and

Figure 4 is a sectional view of a means by which the -requiredconnections to the battery to. be tested may be quickly and accuratelymade.

The invention can be described to best advantage with reference first toFigure 2. The battery to be tested is diagrammatically illustrated at Ias consisting of three cells connected together in series by the usualstraps. Between the terminals 2 and 3 of battery I is connected a mainload circuit 4, which includes a resistance 5 preferably made ofnichrome, or other metal having a, negligible temperature co-eflicientso that, irrespective of the length of timeduring which-the currentflows through the circuit 4, it will remain a definite, fixed value.

Theoretically, this should correspond to the maximum rating of thebattery under test, but, since the ratings of batteries ofdiflerentsizes are diiferent, this is impossible, and, as a practical issuggested that the value of resistance 5 may be that which is suitablefor a standard 15-plate battery since this is the most popular size.Probably 90% or more of all batteries ,in use are either 13, 15 or 17plate. If the testers of this invention is designed for a 15-platebattery it will be found to be substantially as accurate for 13 and17-plate batteries, "and suiiiciently accurate for the smaller and endof the potentiometer, as shown in dotted line.

ranged that they move together and so that they will make contact withcontacts 8 and 9, 9 and I0, or'lll and II. These arms I2 and I3 are theterminals of a circuit which includes a potentiometer I4 consisting of afixed resistance I5, 9. variable resistance I i, and contact arm II. Theresistance of potentiometer I4 is uniform per unit of length, and veryhigh as compared with the resistance of main load circuit 4, so that thevalue of the current diverted from the main load circuit is negligible.For convenience, this circuit will be called the potentiometer circuit.

As a simple explanation let it be assumed that in this circuit thevoltage of each cell of the battery can bedivided into two parts of anydesired relative proportions. At the electrical mid-point the voltage ineach half would be the same and equal to half the voltage of theconnected cell. If the cell were in perfect condition and fully charged,a meter connected across either half of potentiometer I! would indicate.9 volt. This point on the meter scale could be marked100%. Any othercell of the same battery or a cell of another battery of the same size,ifperfect and fully charged, would cause the same meter deflection tothe 100% mark.

However, if an under-charged or defective cell were substituted for theperfect cell, the load on the battery represented by fixed resistance Iwould cause its voltage to drop to a smaller value, and the voltageacross each half of potentiometer I4 would be less. This would berepresented on the meter by correspondingly point by swinging arm I1,say, meter connected between this arm and the right in Figure 2, toincrease the resistance in that part of.the potentiometer until themeter indicates 100 Then the voltage across that part of thepotentiometer would be .9 volt, or one-half the yoltage of a perfectcell. If the voltmeter were now connected across the remaining part ofthe potentiometer II, as indicated in full line in Figure 2, the voltageacross that part would be found to be less than .9 volt because thetotal voltage is less than 1.8 and .9 volt have already been accountedfor as above explained. Since the resistance of potentiometer of length,this voltage instead of being indicated in volts, could be shown on themeter scale as a percentage of 1.8 volts, or, in other words, as apercentage of the terminal voltage of a perfect fully-charged cell.

In other words, the the percentage of deficiency or under-charge.

That the cell is'defective by, say, twenty percent (20%) is somethingnot only the'operator, but the battery owner-can instantly ,understandand appreciate, whereas the knowledge that the voltage of the cell isapproximately 1.45 volts instead of 1.8 volts means absolutely nothingto the average battery owner and little to many of the service man. Noclear picture of condition is immediately presented.

This illustrates the 5 general underlying principle of this tester i. e.,-if.a fixed load is imposed upon the battery and the terminal voltageof each half will be equal of a perfect fully-charged cell,

lower. readings. The readings 'could be re-established at the to theleft with the I4 is uniform per unit reading would show directly testermust be capable of fixed resistance 2!; a switch -of potentiometercircuit to the than the load imposed which-can be. indicated directlyupon the scale of a voltmeter.

Were batteriesall of the same size, no additional apparatus would berequired, but a complication is introduced by the fact that the testingbatteries of, say, from 135 to 300 ampere-ratings, or, in other words,containing from eleven to twenty-three plates as well as or diflerentplate areas. 01 these there are commonly three, the plates of somebatteries being smaller and some larger than the standard. I

To enable the tester to give identical percentage meter indlcations ofcondition for these different batteries; requires a meter circuitsomewhat more complex than the simple circuit assumed above. This willbe called the voltmeter circuit and is shown in Figure 3, which,otherwise, is the same as Figure 2. The voltmeter circuit is connectedto switch arms l2 and I3 and, consequently, across potentiometer I. Itincludes a variable resistance ll consisting of the resistance unit l9and contact arm 20, a

23, 24, 25 and 26, and parallel switch arms 21 and 28. A voltmeter 29and multiplier 20 is connected to switch arms 21 and arm l1 oipotentiometer I4 is connected to contacts 24 and 25. By throwing switcharms 21 and 28 so that they make contact with contacts 22 and 25, thevoltmeter is connected across that part of the potentiometer to the left'0! contact arm 11. Also variable resistance l2, and resistance 2| areincluded in the voltmeter circuit. Or, on the other hand, i! switch arms21 -and 28 are thrown so as to engage contacts 2| and across that part.

26, the voltmeter is connected 4 right of contact arm l1, andvariableresistance l8 and resistance 2| are not included in thevoltmeter circuit.

The purpose of variable resistance I8 is to compensate in the voltmetercircuit for the fact that all batteries tested, regardless of size, areunder the same resistance load resistance 5, so that the voltage acrossthem 22 having contacts 28 and the contact.

substituted and the register 1.8 by means of variable'resistance 18*size of the battery. Similarly; another perfect fully-chargedbattery ofa different size can be voltmeter again made to and the point markedwiththe size of that bat- 1 tery. In this way resistance 18 can becalibrated load, determined by are different even when "they are inexactly the same condition. 'For example, assume that the battery undertest is perfect, but is rated at less on the voltage across each cellwould be less than the standard 1.8 volts. However, if there isresistance in the meter circui the meter can be made to read 1.8 volts,by eliminating some of this resistance. On the other hand, iithe batteryunder test has a higher ratingthan the load imposed by the loadresistance 5, the voltage it by load resistance 5,

for all sizes within the range of the tester and the points at which itsarm 20 is to be set for each size, definitely indicated upon a dialassociated with the resistance.

To test a battery by means of this apparatus,

the six connections to the battery shown in Figure 3 are first made.This will place the load ll across the entire battery when switch T isclosed and also provides for the connection 0! each cell of the batteryto the potentiometer and voltmeter circuits through the agency ofswitch 1. In Flgure'3 the middle cell is connected. Let it also beassumed that contact arm 11 is so positioned that it does not engagewith potentiometer resistance 16 and that switch arms 21 and 28 are incontact with contacts 23 and 25.

The next step is to position the arm 20 of variable resistance l8 at theindicated point on resistance unit 19 for the size of battery undertest. It will be noted that the battery is'not'yet under load ahd nocurrent is flowing in either the potentiometer or voltmeter circuits.

The switch 6 may now be closed, which imposes the load upon the batteryand potentiom eter contact arm l1 moved so that it engages potentiometerresistance" IG. The pointer of voltmeter 29 will then rise and, as arm11 is adjusted on resistance I6, may be made to in-' dicate 100%. Thismeans that the voltage across the voltmeter is .9 volt. The voltageacross that part of the potentiometer H to the left of arm l1 is greaterthan .9 volt by the amount ofvoltage absorbed by resistances l8 and 2|.

across each cell will be higher than 1.8 volts. In

made to read 1.8 by

this case the meter can be I adding the proper amount or resistance-tothe voltmeter circuit. Consequently, the smallbattery and the largebattery cell in the same condition can be made to produce the samedeflec: tion 01 the meter.

Specifically, by positioning arm 2. of variable,

resistance ll at certain predetermined points on the resistance unit I9so that more or less resist ance is included in the voltmeter circuit ofFigure 3, this factor of voltage varlabilitycan be compensated torsothat itwill have no eflect upon the deflection of the meter.These'settinss of variable resistance It can be marked in terms and thesize of the plates of the number'oi plates on a suitable dial associatedwith variable resistance it, so that resistance be set for the size 0!the battery The actual test is now performed by swinging contact arms 21and "of switch 22 so that. they engage with contacts 24 and 28; whichbridges voltmeter 29 across the other part of potentiometer ll to theright of the position of contact arm l1. The voltmeter will indicate theactual voltage across this part of the potentiometer which, of course,is equal to the remaining voltage of the" cell, and, as alreadyexplained,

this indication may berexpres'sed in percentage instead of in actualvoltage.

If the cell is perfect and voltage will be .9 volt and the meter willindicate 100%. II the cell is defective or undercharged,

' the meter indication will be lower and, as already ll can immedlatelyunder test. 79-- explained, can be expressed in a percenta of what thevoltage across the cell would be if it were perfect and fully charged.

, In other-words, to make the meter indicate .9 volt or the voltageacross the left part of potentiometer It must be altered sufllciently tocompensate for/"the eflectof resistances lO and 2|.v Thissubtractsiromor adds to the voltage l8 and fixed resistance fully charged, this feach cell can be noted without even equal to the difference between theactual voltage across the cell and its correct voltage of 1.8 volts whenunder its rated load. It also adds or subtracts an equivalent amount ofthe voltage across the other part of potentiometer I to the right of armI! sothat the voltage across this part can be measured directly by thevoltmeter just as though the batterywere, in fact, discharging atitsrated load.

\ The other cells maybe connected to the potentiometer and voltmetercircuits by throwing switch 1 to close the indicated contacts and thentested by repeating the meter indication for each of the cells is notless than 90%, the battery may be assumed to be in good conditon; if theindications are between 90 and 70%, the condition of the battery may beassumed to be from fairly good to rather poor, but still usable. If theindication for any cell is below 70%, the probabilities are that thecell is defective and the battery should be replaced. However, if theineterindications for all of the cells are 'low, but substantially thesame the battery may be undercharged instead of defective, and it againbefore reached. a

To facilitate the reading of the meter still further, its scale below70% may be colored red. The area between 70 and area above 90% green. Inthis way the .three areas indicating good," fair" and poor" be sharplydefined and the general condition of reading. the percentage scale.

'To'assist in comparing the indication of one cell of the battery withthat of another, the metermay also be provided with a second pointer II,which can be swung manually across the scale by a. knob 49-. When thefirst cell is tested, the pointer 48 may be set to correspond with theresulting meter indication and will assist in the described procedure.It

should be fully charged and tested any decision as to its condition isas a percentage .of

90% yellow, and the of the circuit than would noting the difierencebetween this indication and those for the other two cells.

It has been assumed in the preceding explanations that the terminalvoltage of the battery has been so divided that one part equals .9 voltplus or minus, respectively, any excess or deficiency of the actualterminal voltage above or below the rated terminal voltage of 1.8 volts.In consequence, the other part would actually be .9 volt if the batteryis perfect and fully-charged. However, it will be evidentthat anyfraction of the rated terminal voltage may be combined with the excessor deficiency of the actual 'terminal voltage above or below the: ratedterminal voltage of 1.8 volts, and that the remainder of the terminalvoltage can be shown directly on the meter as a percentage of the ratedterminal voltage. The manner in which the terminal voltage is divideddepends largely upon the electrical characteristics of the circuits andof the excess of the actual terminal voltage of the cell 75 over 1.8volts, or minus any deficiency in the actual terminalvoltage of the cellbelow- 1.8 volts, then the other part will be the remaining fraction ofthe actual terminal voltage, which can be expressed as a percentage of1.8 volts, 1. e., .the rated terminal voltage of the cell under itsrated load.

Since a small difference in voltage indicates a decided difi'erence incondition, it is desirable that the voltmeter be relatively sensitive tovoltage difi'erences when the actual test is made, whereas it may becomparatively insensitive for the preliminaryadjustment. This is madepossible by including resistance or multiplier 2| in series withvariable resistance l8 and giving it than that of the multiplier I avalue much larger 30 Then, when the voltmeter 'is bridged across theleft part of the potentiometer circuit shown in Figure 3 so thatresistance 2| and a part of resistance ll, depending upon the size ofthe cell under test, are included, the meter is, comparatively speaking,a high resistance meter with the characteristic that a given change inthe voltage imposed upon it will produce a compa'ratively small changein its indication. Obviously, to bring its pointer to the 100% mark,much less of potentiometer resistance I 6 would be permissible, and armI! would be positioned nearer the initial end of this res'istance. Whenthe voltmeter is switched across the other part of the potentiometercircuit so that the resistances l8 and U are excluded, the'voltmeterbecomes a comparatively low resistance meter and more responsive tosmallchanges in the resistance of thecircuit.

Resistance I 5 serves a similar purpose in the potentiometer circuit byreducing the required range of resistance l6. In consequence, a givenmovement of contact arm will produce a smaller change in the resistanceotherwise be the case. This feature is of great practical importancesince it permits the making of sensitive adjustments with ease andaccuracy.

The electrical value of the resistance and other devices described abovemay be varied between rather wide limits according to the preference ofthe designer, andcan be determined by should be much those skilled indescription. It the resistance has already been explained that loadcircuit and circuit as compared with I cuit for the same reason.

,on the dial "a, the

Thedevice described above may be mounted behind a panel such as thatshown in Figure 1. In this arrangement a knob 33 operates switch arms l2and I! to connect the left center or right cell of the battery to thepotentiometer circuit and voltmeter circuits. In the position shown andwith the pointer pointingto "Center" middle cell is connected as shownin Figure 3. Switch 1 may also be combined with switch 22 so that knob33. can also be used to switch the voltmeter across one part or theother of the potentiometer circuit, as indicated by the broken line inFigure 3. Preferably the two switches are so connected that, normally,thetwo contact arms of switch 22 will be in contact with contacts 23 and25: as shown in Figure 3, so that nect any one of the three cells of thebattery into the potentiometer circuit without disturbalong resistancel6 the art in the light of the above.

of the potentiometer circuit knob. 33 can be turned to con-- knob 33towards j pointer of knob 34 is turned to point to pushing the panel,switch 22 is shifted to its ot er position inwhich contact is made withcon acts 24 and 23.

Another knob 34 is mounted on the shaft-of tance l3 so that ing thiscondition. Then, by simply contact arm zll'of variable resis by turningthis knob, the unit l3 can be altered as required for battery cells ofdifferent sizes. The for each size of battery maybe indicated by abatteries having small, standard, or large size plates, each ring beingnumbered to indicate the number of plates per cell. For example, if theI3 on the dial ring marked position of knob 34 accuse value ofresistance 10. dial 340., consisting of three concentric rings for 13Standard, the resistance 1 l3 will then be properly set for the testingof a standard 15 plate battery.

The dial 35 of voltmeter 29 marked in percentage, asshown,

v is also observable through an opening in the panel and may be goinstead of volts..

Below the meter 23 is shown another large knob 33, which may serve Icontrolling the main load circuit switch 3 and potentiometer contact armH, as indicated by thedotted line 60. in Figure3. When this knob isturned to its extreme counter-clockwise posi tion, switch 3 is open, asshown in Figure 3, and potentiometer arm I] is alsoout of contact withpotentiometer resistance It, so that the poten-' tiometer and voltmetercircuits are alsoppen. By turning knob 33 in clockwise direction;potentiometer arm i1 is brought into contact with h the endofpotentiometer resistance l6. A slight turn closes switch 6 to completethe 35 additional main load circuit and further turning moves con tactarm l'l along potentiometer resistance l3.

the dual purpose of the battery by means of the two clips In this waythe numberof control knobs isireduced to three. The various switchesmay, if desired, be separately controlled, but the combining of controlsin -this way greatly simplifies the panel and reduces the likelihood oferror in making the necessary adjustments.

The making of the six required connections to one battery may be greatlyfacilitated by using the clips 31 shown in Figures 1 and 4. They aresimilar, so that only one will be described: It consists essentially ofa handle 33 of rubber, or other insulating material, within whlch issecured in any desired way a contact member 33 termio pointerrests atthe one.

nating in an offset. end 43 projecting beyond the handle and having anopening 4| somewhat larger than the terminal post of a storage battery.A heavy wire or cable 42 capable of carrying the main load current withease is connected to contact member 39and runs toone end of main loadresistance 5 (see Figure 3) on contact member 39, but insulatedthei'efrom, is also mounted another contact member 43, one end of whichalso projectsbeyond the end of contact member 33 and slightly beyond theedge of opening 4]. Contact member 43 isalsoconne'cted to rawire 44which, as shown in Figure 3, runs to contact I] of switch I. Alsomounted on contact member 33 andalso insulated therefrom is a thirdUshaped contact member 45 made of highly resilient metal, terminating ina sharpoint46, which as shown in Figure 3 is connected contact III ofswitch 'I by wire 41.,

The connection to the. battery by rneans of this .clip is made byforcing point 46 of contact.mem-

3a of the battery and then 'ber'45 into strap passingterminal post a ofthe battery through opening 4| of contact member 33. The resilience ofcontact member 45 will cause the clip to tilt .75-

so thatpost 3' of battery will be jammed between the edge of opening 4|and the end of contact member 43'. By thissimple operation the threerequisite connections to the battery are made.

The other clip terminal 2 and strap same way to make connection betweenbattery terminal 2 and the Ether, end of main load resista'nce 5, andalso between terminal tactB of switch 1 and strap of switch 1. .1nstandard commercial batttries 2 and conthe negative post. Therefore, theopening 4! in contact member 39 of the clip by which the "batteryshould, preferably,

than the similar opening of the other clip so that it cannot passoverthe positive post. In this way reversal of the connections to thebattery is 'made impossibla With the tester arranged as above described,the testing of the battery becomes a very simple matter. The operatorfirst connects the tester to 31. Having be a little smaller ascertainedthat the battery is, say, ,15-plate battery, he turns the knob 34 sothat it points to 15 on the middle ring marked Standard of dial 34a. Hethen turns knob, 33, say, to the point marked Left, which connects theleft cell of the battery to will be assumed is in its extremecounter-clock! wise position,is then turned in clockwise direction,which first causes potentiometer arm ll to engage with potentiometerresistance 16, and

then closes the main load circuit switch '6. The

pointerZBa of meter 29 will begin to move from its zero position and theoperator will continue to turn the tester control knob. 35 until themark indicating Then knob 33 is pressed and the meter will-indicate the'percentage of deficiency or undercharge of the cell. The middle cell canthen be tested by turning knob 33 to the Center" position and repeatingthe operations outlined above. The right cell can also be tested in asimilar manner.

The .operation of this tester is not only ex- I tremely simple, but theindicated results are re- :liable and immediately No reference to tablesgiving the ratedload for tionnecessary is the sifie of the battery, andthis is usually marked upon the battery itself; Be-

cause of these features the danger of reaching incorrect conclusionsfrom the test is substantially eliminated. Furthermore, the tester iswell adapted to quantity production at low cost and its upkeep isnegligible. Consequently, it makes battery testing service available atmany garages or minus respectively any excess or" deficiency of itsterminal voltage in' relation toits rated 31 is similar and isapplied-to 3b of. the battery in'the- "3b and contact 9 the positivepost is always a little larger than tester is connected to the negativepost of the.

a standard.

I the potentiometer circuit. The tester control knob 36,-which itunderstandable by anybatteries of diflerent sizes or other informa 7'tion is required. The only extraneous informav voltage, and meansfordetermining the value of sistance in series,

ing the load'circuit and a first of points to the circuit containingvoltmeter and the cell. I

2. A device for testing storage batteries oi the same rated voltage butof diil'erent rated amincludes a load circuit value connectible acrosspere capacities, which having aflxed resistance han I 1 rated voltagesbut the battery, a circuit including a potentiometer or voltage dividerconnectible across any cell of the battery, a contact arm adapted tomake contact with any point of said potentiometer, a a

circuit containing a voltmeter and a variable revoltmeter and .saidcontact arm and to one end of said potentiometer, and for connectingsaid voltmeter without said variable resistance to said arm and to the'other end of said potentiometer.

3. A device for testing storage batteries as delined in claim 2, inwhich the resistance of the potentiometer circuit is much higher thanthe resistance of the load circuit and the resistance of the voltmetercircuit is much higher than the resistance of the potentiometer'circult.

4'. A device for testingstorage batteries oi. the

- same rated-voltages but of diflerent rated ampere' capacities, whichincludes a load circuit having a fixed resistance value connectiblebetween the positive and negative terminals of the battery, {our contactpoints, a clip for connect- I g the contact points to the positiveterminal or the battery and also for connecting a second 0! the contactnegative terminal-oi the same cell means for connecting said variableresistance to said.

and the positive terminal of the third cell and also for connecting afourth of the contact points and the load circuit to the negativeterminal of including a potentiometer, said potentiometer circuitadapted to simultaneously connect said first and second, third, andthird and fourth contact points, respectively, to the opposite endsofsaid potentiometer, a contact'arm adapted to make contact? any pointof said potentiometer, a I a voltmeter and a variable resistance inseries, means torconnecting said said variable resistance to saidcontact arm and to one end of said potentiometer and for connecting saidvoltmeter alone to said contact arm and to the other end 01' saidpotentiometer.

' 5. A device for. testing storagebatteries as defined in claim 4, whichincludes a switch'in the operating is the same as the means forconnectingfithe battery into two parts, one of which is 6. The method oftesting batteries of the same or difierent' rated ampere capacities,which consists oi applying a load oif fixed resistance value across thebattery, dividing the voltage of a cell of the battery into two parts,one or which is equalto half the rated voltage of the'cell plus orminus, respectively, any excess or deficiency of the terminal voltage ofth cell in relation to its rated voltage and then determining the valueob the other part of the terminal voltage oi. the cell as a percentage01' its rated terminal voltage when under its rated load.

7. The method of testing the cells'oi storage batteries of the samerated voltages but of different rated ampere capacities, oi app ying aload of fixed resistance value across the battery, dividing the terminalvoltage oi a cell of said battery into two parts, one of which as apercentage of 1.8 volts.

8. The method 01' testing storage batteries having a rated voltage underrated load oi 1.8 volts per cell, which consists of placing the batteryunder a load of fixed resistance value, then dividing the terminalvoltage 01 the cell into two parts, .one of which is minus,respectively,

equal to .9 volt plus or any excess or deficiency- 01' the terminalvoltage of the cell in relation to its rated voltage-and thendetermining the voltage of the other part as a percentage of 1.8 volts.

9. The method of testing storage batteries of the same rated voltagesbut oi difierent rated ampere capacities, which consists oi'applying aload of fixed resistance value across the battery, dividing the terminalvoltage of a cell of said equal to a known percentage 01' the ratedterminal voltage oi the cell plus or minus, respectively, any excess ordeficiency of the terminal voltage of the .cellabove or below itsvoltage and then determining the value of the remaining part of theterminal voltage of the cell as a percentage of the rated terminalvoltage of the-cell.

10. The method '01 testing storage batteries having a rated voltageunderrated load of 1.8

volts per cel1,-which consists of placing the batte'ry under a load offixed resistance value, then age of 1.8 volts plus or minus,respectively, any excess or deficiency oi the actual terminal volt-. ageof the cell in relation to its rated terminal voltage and thendetermining the voltage of the other part as a percentage of 1.8 volts.

BENJAMIN F. w. HEYER.

which consists rated terminal

